Vibrator test circuit



M. E. NULSEN VIBRATOR TEST CIRCUIT May 10, 1949.

Filed Nov. 21, 1944 r INVENTOR. flarmn 1 llu/sen Patented May 10, 1949VIBRATOR TEST CIRCUIT Marvin E. Nulsen, Indianapolis, Ind., assignor toI. R. Mallory & 00., Inc., Indianapolis, Ind., a corporation of DelawareApplication November 21, 1944, Serial No. 564,529

The present invention relates to vibrator test.

circuits, and, more particularly, to an electronic direct-readinginstrument for measuring the time efilciency and the contact-dwellbalance of vibratory electro-magnetic interrupters,

As those skilled in the art know, in determining the operatingcharacteristics and the contact ad justment of vibratory interrupters,accurate measurement of certain factors connected with the periodsduring which the contacts are closedis of primary importance. Suchfactors are, for example, the time efficiency, that is the contactdwellperiod as a percentage of the cycle period for each pair of contactsindividually; the overall time efliciency, that is the sum of thecontactdwell periods of the two pairs of contacts as a percentage of thecycle period; and the contact balance figure, indicating the-ratio ofthe time efliciencies of the two pairs of contacts. Prior suggestions inthis direction included connecting a DArsonval type meter in series withthe vibrator contacts, said meter operating as a timeaveraging type ofcurrent measuring instrument. Test circuits of this type, however, hadserious limitations in that their use was restricted to testingdriver-contact type vibrators. They were unable to yield accurateresults in the case of shunt-coil type vibrators because the coilcurrent, a quantity which varies widely during the entire time the pullcontacts are open, would also be recorded by the meter and therebyrender the meter reading useless as a direct measure of time efficiency.Attempts were made at various times to compensate for the errorintroduced by the coil current, either by calculation or by introducinga similar coil across the other pair of vibrator contacts. However, ofthese suggestions and proposals, none was completely satisfactory andsuccessful on a practical and industrial scale.

It is an object of the present invention to provide a vibrator testcircuit which eliminates the foregoing difficulties inseparablyconnected with the construction and operation of prior devices of thedescribed character.

It is another object of the present invention to provide adirect-reading instrument for rapidly and accurately determining thetime efllciency and the contact-dwell balance of the contacts ofelectro-magnetic vibratory interrupters, including both driver-contactand shunt-coil type vibrators.

It is a further object of the invention to provide an electronicmetering device for the instantaneous and accurate measurement of thetime efficiency of the contacts of vibratory interrupters 4 Claims. (Cl.175-183) 2, of any desired type, such measurement being carried outunder actual conditions of load current encountered during the normaloperation of the vibrator.

The objects of the invention include direct measurement of the timeefliciency of the rectifier contacts, and also ready determination ofthe time difierenti'al between interrupter and rectifier contact-dwellperiods, in a vibratory electromagnetic interrupter.

It is also within the contemplation of the invention to provide ametering device of improved character for measuring the time efficiencyof vibratory interrupters, said device being adaptable to carrying outthe desired measurements on vibrators which may be of difierenttype ormay have difierent operating voltages.

The invention also contemplates a universal metering device for vibratortime efficiencies which is very simple in construction, reliable inoperation, and which may be readily manufactured and sold at a low cost.v

Other and further objects and advantages of the invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawing; in which Fig. 1 is the circuit diagram of apreferred form of circuit organization of the device embodying thepresent invention, together with the circuit of a self-rectifyingvibrator of the shunt-coil type; and

Fig. 2 is the circuit of a driver-contact vibrator.

While a preferred embodiment of the invention is described herein, it iscontemplated that considerable variation may be made in the method ofprocedure and the construction of parts Without departing from thespirit of the invention. In the following description and in the claims,parts will be identified by specific names, for convenience, but theyare intended to be as generic in their application to similar parts asthe art will permit.

Broadly stated, in accordance with the principles of the invention, thetwo contacts of the pair of cooperating vibrator contacts, the timeefliciency of which is to be measured, are respectively connected to thecathode and grid of an electron tube, such as a suitable triode, and arealso arranged to open and close a circuit, which imposes at leastcut-off grid potential on the more negative contact from the instant ofmoval of the said cut-off potential from the grid. In that case, theplate current, which only flows while the contacts are closed, and doesso at a constant rate, constitutes a measure of the dwell period of thecontacts in question. Likewise, the absenceof plate current constitutesa measure of the non-contacting period of the contacts. A current meterof the DArsonval type, giving a time-averaging reading, will hencerecord the ratio of the dwell period to the sum of the dwellandnon-contacting periods, which is the time efliciency of the contacts.Thus, the meter may be directly calibrated in per cent time efllciency,permitting direct and instantaneous reading of this quantity. It ispreferred to provide an electron tube circuit of the described type foreach of the two pairs of contacts of the vibrator whereby it is madepossible to directly determine the time efllciency of each-contact pairand also the overall time efliciency of the vibrator. device may becombined with suitable sockets adapted to receive and to hold vibratortypes and with switching means .for selectively carrying out themeasurementfor the interrupter and for the rectifier contacts ofsynchronous vibrators, for

The

applying different operating voltages to the'vibrator, etc., as it willinafter. V

Referring now more. particularly to Fig. 1 of the drawing, referencecharacter it] denotesv a vibrator socket of suitable type adapted tomatch the vibrators to be tested, and having jacks II to IE mountedtherein. Of these, .jacks i2 and. i

appear more fully 'here- 5 I -comprises 100 graduations, numbered atintervals 4 contact arms 53 and 54 or two contact selector switches 55and 56, respectively. Switch 55 has three contacts adapted to cooperatewith its switching arm, of which 51 is connected to jack I2, 58 isconnected to jack II, and 59 is grounded. Switch 56 has likewise threecontacts, 60, BI, and 62, of which 60 is connected to jack l5, contactBI is c-onnectedto jack M5, and contact 62 is grounded. Contact arms 53and 54 are connected for joint rotation by means of a shaft 53.5

Plates 48 and 49 of the tubes are connected to the positive terminal ofa B battery 64 through a meter 65 and through adjustable resistances '66and 61 and through contactor keys 68 and 69, re-

spectively. The negative terminal of batteiy 54 is grounded. Battery 54may have a voltage of 22 volts and resistances 55 and 51 may benoninductive potentiometers having a resistance of 10,000 ohms each. Ofcourse, both battery 64 and direct current source may be provided in theformer properly filtered power supply units of suitable type, operationof which may be initiated by filament switch 50 at the same time whenthe heater circuits of tubes 40 and 4| are closed.' Meter 65 is aDArsonval type instrument of the type that indicates the timeaveragingvalue of the current. Its scale preferably 5 from 0 to 100, thus readingtime efliciency directare respectively connected to the two ends of acenter-tapped interrupter circuit load resistance l1, and jacks II andI6 are respectively cone nected to the two ends of a center-tappedrectifier circuit load resistance l8, -Resistance I! is of a relativelylow value, such as forjexample 5 ohms, while resistance 18 may have avalue of 250 ohms. .Jack I4 of the s'ocket is grounded, and jack I3 isconnected to contact arm [9 of arotary tap switch 20,having'contactsfl2l, 22, '23,

and 24. Contact-2| of these is disconnected, and

contacts 22, 23, and 24 are respectively connected to taps 2'6, 21 and28 of a source of direct current 25, the positive terminal of which isgrounded. A similar rotary tap switch 30 has its contact arm 3|connected to the center taps of both resistances I! and I8 and hascontacts 32,

33, 34and 'ofwhich 32 is disconnected and contacts 33, 34 and 35 arerespectively connected to taps 28, 29 and to the negative terminal ofthe.

source. -It will be noted that sourceof current 25 has been illustratedas an 8-cel1 storage battery, the voltage difference. between taps 26,21 and 28 being one cell, while the voltage difference between taps 28,-29 and the negative terminal is two cells. Contact arms l9 and 3l areconnected fortjoint'operation bymeans of a shaft, diagrammaticallyindicatedfby dotted line 56. A voltmeter 31 is connected between thecenter tabs of resistances I! and l8 and ground through a seriesresistance 38 and indicates at all times the operating voltage appliedto the 'vibrator under test. i

The metering circuit comprises a'pair of triodes 40 and 4i,-havingheaters and 43, cathodes 44 and 45, grids 46 and 41, and plates 48 and49, respectively. .One end of both heaters is grounded, and the otherend thereof is connected to tap of source 25 through a switch. 50.Catho'des- 44 and are both. grounded and grids 46.

ly in per cent.

be readily understood by those skilled in the art.

To calibrate the instrument, first filament switch 50 is closed, closingthe heater circuits of tubes 40 and 4|, and contact selector switchesand 5B are set to their calibrating position in which their switchingarms 53 and 54 make with contacts 59 and 62, respectively. In thisposition,

grids 4'6 and 41 are at cathode or ground potential, permitting the flowof plate current. Contactor key 58 (A) is now held closed and resistance6'6 is-adjusted until full deflection of meter is obtained. Contactorkey 68 is nowreleased and key 69 (B) is closed, while its resistance 61is adjusted until full-scale deflection of meter '55 is obtained. Thedevice is now calibe tested is plugged into socket l0. Of course, a

brated and ready for use. i

To measure the time efiiciency, the vibrator to '15 of which-l3 and.'|5are connect-ed to relative- I ly stationary interrupter contacts 11 and18, re-

and .41 are respectively-connected through resistances 5| and 520i about20,000 ohms each to spectively, and pins-12, 15 are connected tostationary rectifier contacts 79 and 8ll,'respectively.

It will be understood that the vibrator is shown schematically so thatthe auxiliary contacts normally provided on the reed do not appear inthe drawing. However, the expression set of contacts in the appendedclaims is intended to refer to any one of the contacts shown, as forexample contact 18, .together with the auxiliary contact or othercontact means provided on the reed. In a broader sense,'the expressionset of contacts may, of course, refer to any pair of contact membersproperly connected to the socket I0. Pin 14 is connected to reed 8ibearing vibratory contacts cooperating with the said stationarycont-acts (not shown) and a shunt coil 82 is device ofthe inventionemploys non-inductive resistances as loads rather than the conventionalcenter-tapped transformer. The absence of the conventional center-tappedtransformer makes necessary the use of double the rated voltage of thevibrator under test in order that the voltage applied to the shunt coil,and hence the reed amplitude, be substantially the same as when atransformer is used. Shunt coil 82 will now be energized through itsconnection to the reed grounded through pin 14 and jack l4 and thusconnected to the positive terminal of source 25, while its other endthrough pin I3 and jack l2, the upper half of resistance I'I, switchingarm 3!, and one of contacts 33 to 35 is connected to the correspondingnegative terminal of the source. Reed 8| will be deflected until itcloses interrupter contact 11 and shunts coil 82 and at the same timepasses current through the upper half of the said resistance II. Thedeflected reed will now pass through its neutral position and closes theother interrupter contact 18, thereby passing smaller of readings A andB to the larger is the percentage balance of the two pairs of contacts Aand B.

To carry out the same measurements for the rectifier contacts, contactselector switches 55 and 56 are adjusted to their rectifier position inwhich they respectively make with contacts 58 and BI, thus connectingthe ends of rectifier load resistance I8 to the grids of tubes 40 andII. Repeating now the steps carried out for the interrupter contacts,the readings will correspond to the time efficiencies of the respectiverectifier contacts, instead of the interrupter contacts.

From the results of\ the foregoing measurementsv on the interrupter andrectifier contacts, the time-differential percentage of the vibrator maybe easily determined, this being the differ-'- ence between the timeefilciency of a givenpair of'interrupter contacts and that of the corre-I vibrator, such as the vibrator 9i shown in Fig. 2

current through the lower half of resistance I1,

through pin I5 and jack I5. Thus, the reed will be maintained incontinuous vibratory motion in a manner well understood, alternatelypassing current through the two halves of interrupter circuit loadresistance I1. During vibration of the reed, it will also alternatelyground rectifier contacts 19 and 80, respectively connected to the twoends of rectifier load resistance I8 through the corresponding base pinsof the vibrator and jacks of the socket. Therefore, rectifier loadcurrent will be alternately passed through the two halves of the saidresistance I8. In order to closely simulate actual load conditions,resistance I1 is so determined as to have about 5 amperes flowingthrough the interrupter portion of the circuit and resistance I8 is sodetermined as to have about 0.1 ampere flowing through the rectifierportion of the circuit. These currents can, of course, be increased ordecreased as desired. To carry out the measurement of the timeefiiciency of the interrupter contacts, contact selector switches 55 and56 are turned to their interrupter position in which they make withcontacts 51 and 60, respectively, and connect the two ends of loadresistance IT to the grids of tubes and 4|. It will be noted that thiswill apply negative potential beyond cut-off to the grids when theinterrupter contacts are open and will apply cathode potential to thegrids when the said contacts are closed, Thus, the integrated platecurrent flowing through the tubes will be proportional to the ratio ofclosed contact period to the full cycle. Therefore, upon closing key A,the meter reading will be the time efficiency of interrupter contactsand comprising base pins 92 to 95, of which 92 and are respectivelyconnected to relatively stationary interrupter contacts 96. and 91, pin94 is connected to reed 98, and pin 93 is connected to one end of adriver coil 99. The other end of coil 99 is connected to a drivercontact I09, normally making with reed 98. When this vibrator is pluggedin into socket I0, its pins 92 to 95 will be respectively engaged byjacks I2, I3, I I, and I5 of'the socket. It will be noted from Figs. 1and 2 that in this case reed 98 will be connected to thepositiveterminal of direct current source 25. contacts 96 and 91 (A and B) willbe connected to the two ends of interrupter circuit load resistance I1and the end of driver coil 99 will be connected to switching arm I9 ofcell selector switch 20. Cell selector switches 29 and 30 Will be set inaccordance with the rated voltage of the vibrator under test. It will benoted that switch 20 supplies the-rated voltage to the driver coil, incontrast to the case when shunt-coil type vibrators are tested, wheredouble of the rated voltage is supplied to the shunt coil. As one endofdriver coil 99 is connected to the positive terminal of the sourcethrough contact I90, reed 98, ground pin 94, and jack I 4, and the otherend of said coil is connected to a negative tap of the source throughswitch 29, jack I3, and pin 93, the reed will be maintained incontinuous vibration, and current will be alternately passed through thetwo halves of load resistance I'I. Now the measurement of timeefficiency of interrupter contacts A and B may be carried out in thesame way as it has been described in the foregoing. Of course, vibrator9! may be likewise provided with rectifier contacts, which can bechecked as to their time eiliciency same as the rectifier contacts ofshuntcoil vibrator! I.

Tubes 40- and 4| may be triodes of any suitable type, such as, forexample, a 6SN'7GT twin triode, in which case grid current limitingresistances 5| and 52 may be omitted. It has been found, however thatwhen using such triodes of the high-vacuum type, the time efliciencyreadings were slightly low. This was traced to the fact that even thougha touching pair of vibrator contacts be connected respectively to thecathode and grid of the triode, the grid is at a slightly the associatedleads, when these elements are carrying current. Obviously, this slightreduction in grid potential causes the plate current to be less duringthe time the contacts are touching than the full scale meter reading towhich the plate current was previously adjusted when thecontact-selector switch was in the calibrating position, where the gridwas directly connected to the cathode.

This difiiculty may be eliminated by using tubes in which the platecurrent is independent of small negative grid potential swings away fromthe cathode potential. Thus, excellent results were obtained with a pairof type 884 Thyratron gas-filled tubes, connected as indicated in Fig,1, wherein resistances 5| and 52 are interposed in the grid circuits tolimit the grid current. By employing relatively low plate voltages, ofthe order of 22 volts, and relatively high negative grid potentials, ofthe order of 7.9 to 17.6 volts, it is assured that the grid will retaincontrol over the plate current at all times. This is in contrast to theconventional operation of tubes of this general type with high platevoltages, where the grid loses control over the plate current once theflow of plate current has been initiated.

In some cases, it has been found desirable to eliminate the B-batteryand to supply an A. C. voltage to the plates of the Thyratron tubes.This has the advantage that the grids of the tubes will retain theircontrol over the plate current at much lower grid voltages, such as maybe encountered when testing vibrators having an operating voltage lowerthan 6 volts. Preferably, the plates are supplied with an alternatingvoltage of a frequency which is high enough to have the time of a platecurrent pulse constitute a negligible percentage of the vibratorcontact-dwell period and still not high enough to have the time betweenpulses shorter than the deionization time of the tube. Thus, analternating voltage of 12,000 to 15,000 cycles per second providesexcellent results, such voltage being obtained, for example, from asuitable audio-frequency oscillator.

It will be noted that the principles of the inven tion provide variousadvantages. First of all, the device of the invention permits thedetermination of the time efiiciencies of vibrators of any desired typeand of any desired voltage rating under actual and normal load-currentconditions. The time efficiency, including the overall time officiency,is directly and instantaneously read on the meter without the necessityof any calculation or conversion. As the grid currents of the tube arenegligible compared to the operating currents in the interrupter andrectifier circuits, the measuring circuit has absolutely no efiect uponthe load conditions or upon the wave form of the vibrator under test.Moreover, the device of the invention is extremely simple inconstruction and may be manufactured at a very low cost so that it maybe advantageously used not only in manufacturing practice and indevelopment work but also by servicemen for testing the relevantoperating characteristics of vibrators now used on a substantial scalein all kinds of mobile communication equipment.

Although the present invention has been described in connection with apreferred embodiment thereof, variations and modifications may beresorted to by those skilled in the art without departing from theprinciples of the present invention. All of these variations andmodifications are considered to be within the true spirit and scope ofthe present invention, as disclosed in the foregoing description, anddefined by the ap pended claims.

What is claimed is: 1. A testing arrangement for a vibrator including areed, a pair of contacts cooperating with said reed and electromagneticdriving means for.

a control grid, a connection between one of said contact terminals andsaid control rid, a connection between said reed terminal and saidcathode, and an indicator of the average current type connected in theanode circuit of said tube, saidtube bein biased to cut off when saidload is disconnected from said source..

2. A testing arrangement for a vibrator including a reed, a pair ofinterrupter contacts, a pair of rectifier contacts, each of said pairsof contacts cooperating with said reed, and electromagnetic drivingmeans for said reed; comprising at least two pairs of contact terminalsadapted to be respectively connected to said contacts, a reed terminaladapted to be connected to said reed, a first load having its endsconnected to the contact terminals for said interrupter contacts, asecond load having its ends connected to the contact terminals for saidrectifier contacts, a source of direct current having its positive poleconnected to said reed terminal and its negative pole connected to amid-point of each of said loads, a tube having an anode, a cathode and acontrol grid, connective means including a selective switch between saidcontact terminals and said control grid for selectively connecting acontact of either said interrupter contacts or said rectifier contacts,a connection between said reed terminal and said cathode, and anindicator of the average current type connected in the anode circuit ofsaid tube, said tube being biased to out 01f in the open position ofsaid contacts, said indicator measuring the dwell period of the contactselectively coupled to said rid.

3. A testing arrangement for a vibrator including a reed, a pair ofcontacts cooperating with said reed and electromagnetic driving meansfor said reed; comprising a pair of contact terminals adapted to berespectively connected to said contacts, a reed terminal adapted to beconnected to said reed, a load having its ends connected to said contactterminals, a source of direct current having its positive pole connectedto said reed terminal and its negative pole connected to a mid-point ofsaid load, a pair of tubes each having an anode, a cathode and a controlgrid, connective means including a selective switch between said contactterminals and each of said control grids for selectively coupling one ofsaid pairs of contacts to the grid of one of said tubes and the otherone of said pairs of contacts to the grid of the other of said tubes, aconnection between said reed terminal and said cathode, and an indicatorof the average current type connected in a circuit common to the anodecircuit of each of said tubes, said tube being biased to cut oil whensaid load is disconnected from said source.

4. A testing arrangement for a vibrator including a reed, a pair ofinterrupter contacts, a pair of rectifier contacts, each of said 75pairs of contacts cooperating with said reed,

mid-point of each of said loads, a pair of tubes I each having an anode,a cathode and a control grid, connective means including a selectiveswitch between contact terminals for one-of said interrupter contactsand one of said rectifier contacts and a control grid for'one of saidtubes for selectively coupling either said one interrupter contacts orsaid one rectfier contact to the grid of said one tube, similarconnective means including a selective switch between the remainingcontact terminals and the rid of the other one of said tubes forselectively coupling either of the remaining one of said interruptercontacts or the remaining one of said rectifier contacts to the grid ofthe other one of said tubes, a connection between said reed terminal andsaid cathode, an

anode circuit for each of said tubes, a portion of each of said anodecircuits being common to both, an indicator of the average current typeconnect'ed in said common portion, said tubes being biased to cut offduring the open position of said contacts, said indicator measuring thedwell period of the contacts selectively coupled to said gridsrespectively.

MARVIN E. NULSEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Re. 15,469 Heising Oct. 17, 19221,340,936 Conway May 25, 1920 1,560,727 Pruden Nov. 10, 1925 1,677,157Weaver July 17, 1928 1,795,656 Massonneau Mar. 10, 1931 1,931,558Saunders Oct. 24, 1933 2,244,338 Krebs June 3, 1941 2,248,545 McConnellJuly 8, 1941 2,254,175 Eltgroth Aug. 26, 1941 2,261,010 Weise Oct. 28,1941 2,287,174 Heising June 23, 1942 OTHER REFERENCES Morecroft,Electron Tubes, John Wiley and Sons, Inc., New York.

